#include <iostream>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <string>
#include <unistd.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <ctype.h>
using namespace std;
const int basesize = 1024;
const int argvnum = 64;
const int envnum = 64;
// 全局的命令⾏参数表
char* gargv[argvnum];
int gargc = 0;
// 全局的变量
int lastcode = 0;
// 我的系统的环境变量
char* genv[envnum];
// 全局的当前shell⼯作路
char pwd[basesize];
char pwdenv[basesize];
// " "file.txt
#define TrimSpace(pos) do{\
while(isspace(*pos)){\
pos++;\
}\
}while(0)
string GetUserName()
{
    string name = getenv("USER");
    return name.empty() ? "None" : name;
}
string GetHostName()
{
    string hostname = getenv("HOSTNAME");
    return hostname.empty() ? "None" : hostname;
}
string GetPwd()
{
    if (nullptr == getcwd(pwd, sizeof(pwd))) return "None";
    snprintf(pwdenv, sizeof(pwdenv), "PWD=%s", pwd);
    putenv(pwdenv); // PWD=XXX
    return pwd;
    //string pwd = getenv("PWD");
    //return pwd.empty() ? "None" : pwd;
}
string LastDir()
{
    string curr = GetPwd();
    if (curr == "/" || curr == "None") return curr;
    // /home/whb/XXX
    size_t pos = curr.rfind("/");
    if (pos == std::string::npos) return curr;
    return curr.substr(pos + 1);
}
string MakeCommandLine()
{
    // [whb@bite-alicloud myshell]$
    char command_line[basesize];
    snprintf(command_line, basesize, "[%s@%s %s]# ", \
        GetUserName().c_str(), GetHostName().c_str(), LastDir().c_str());
    return command_line;
}
void PrintCommandLine() // 1. 命令⾏提⽰符
{
    printf("%s", MakeCommandLine().c_str());
    fflush(stdout);
}
bool GetCommandLine(char command_buffer[], int size) // 2. 获取⽤⼾命令
{
    // 我们认为：我们要将⽤⼾输⼊的命令⾏，当做⼀个完整的字符串
    // "ls -a -l -n"
    char* result = fgets(command_buffer, size, stdin);
    if (!result)
    {
        return false;
    }
    command_buffer[strlen(command_buffer) - 1] = 0;
    if (strlen(command_buffer) == 0) return false;
    return true;
}
void ParseCommandLine(char command_buffer[], int len) // 3. 分析命令
{
(void)len;
memset(gargv, 0, sizeof(gargv));
gargc = 0;
// "ls -a -l -n"
const char* sep = " ";
gargv[gargc++] = strtok(command_buffer, sep);
// =是刻意写的
while ((bool)(gargv[gargc++] = strtok(nullptr, sep)));
gargc--;
}
void debug()
{
    printf("argc: %d\n", gargc);
    for (int i = 0; gargv[i]; i++)
    {
        printf("argv[%d]: %s\n", i, gargv[i]);
    }
}
// 在shell中
// 有些命令，必须由⼦进程来执⾏
// 有些命令，不能由⼦进程执⾏，要由shell⾃⼰执⾏ --- 内建命令 built command
bool ExecuteCommand() // 4. 执⾏命令
{
    // 让⼦进程进⾏执⾏
    pid_t id = fork();
    if (id < 0) return false;
    if (id == 0)
    {
        //⼦进程
        // 1. 执⾏命令
        execvpe(gargv[0], gargv, genv);
        // 2. 退出
        exit(1);
    }
    int status = 0;
    pid_t rid = waitpid(id, &status, 0);
    if (rid > 0)
    {
        if (WIFEXITED(status))
        {
            lastcode = WEXITSTATUS(status);
        }
        else
        {
            lastcode = 100;
        }
        return true;
    }
    return false;
}
void AddEnv(const char* item)
{
    int index = 0;
    while (genv[index])
    {
        index++;
    }
    genv[index] = (char*)malloc(strlen(item) + 1);
    strncpy(genv[index], item, strlen(item) + 1);
    genv[++index] = nullptr;
}
// shell⾃⼰执⾏命令，本质是shell调⽤⾃⼰的函数
bool CheckAndExecBuiltCommand()
{
    if (strcmp(gargv[0], "cd") == 0)
    {
        // 内建命令
        if (gargc == 2)
        {
            chdir(gargv[1]);
            lastcode = 0;
        }
        else
        {
            lastcode = 1;
        }
        return true;
    }
    else if (strcmp(gargv[0], "export") == 0)
    {
        // export也是内建命令
        if (gargc == 2)
        {
            AddEnv(gargv[1]);
            lastcode = 0;
        }
        else
        {
            lastcode = 2;
        }
        return true;
    }
    else if (strcmp(gargv[0], "env") == 0)
    {
        for (int i = 0; genv[i]; i++)
        {
            printf("%s\n", genv[i]);
        }
        lastcode = 0;
        return true;
    }
    else if (strcmp(gargv[0], "echo") == 0)
    {
        if (gargc == 2)
        {
            // echo $?
            // echo $PATH
            // echo hello
            if (gargv[1][0] == '$')
            {
                if (gargv[1][1] == '?')
                {
                    printf("%d\n", lastcode);
                    lastcode = 0;
                }
            }
            else
            {
                printf("%s\n", gargv[1]);
                lastcode = 0;
            }
        }
        else
        {
            lastcode = 3;
        }
        return true;
    }
    return false;
}
// 作为⼀个shell，获取环境变量应该从系统的配置来
// 我们今天就直接从⽗shell中获取环境变量
void InitEnv()
{
    extern char** environ;
    int index = 0;
    while (environ[index])
    {
        genv[index] = (char*)malloc(strlen(environ[index]) + 1);
        strncpy(genv[index], environ[index], strlen(environ[index]) + 1);
        index++;
    }
    genv[index] = nullptr;
}
int main()
{
    InitEnv();
    char command_buffer[basesize];
    while (true)
    {
        PrintCommandLine(); // 1. 命令⾏提⽰符
        // command_buffer -> output
        if (!GetCommandLine(command_buffer, basesize)) // 2. 获取⽤⼾命令
        {
            continue;
        }
        //printf("%s\n", command_buffer);
        ParseCommandLine(command_buffer, strlen(command_buffer)); // 3. 分析命令
        if (CheckAndExecBuiltCommand())
        {
            continue;
        }
        ExecuteCommand(); // 4. 执⾏命令
    }
    return 0;
}
